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Old 05-27-2004, 11:18 PM   #1
bigt61
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What does the Idle screw do? Technical answers wanted

Hey guys,

I adjusted my idle screw and installed a new IACV yesterday because my old one went out. I was driving around today, and all of a sudden i get a high pitched sound, AGAIN after i replaced everything, as i describe in this thread...

http://preludepower.com/forums/showthread.php?t=200414

SlipSlap says it sounds like an air leak and it is whistling. So, i checked everything with intake cleaner... nothing happened. So, i continue to drive along my merry way putting up with the squealing nouse, not knowing where its problem lies, then about 20 minutes later my car starts idling erratically, so i pull over and check it out. I check the ECU, and get code 14, electronic air control. This is 2 times in a row with the same problem, and i just got a new IACV.

My question is this- does the idle screw have anything to do possibly with my IACV's going bad? Does screwing it in mess with the IACV in ANY way? It was about half way out when i screwed it in the first time to get the idle right then reconnected the IACV, and reset the ECU. Have I done something wrong?
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Old 05-28-2004, 12:19 AM   #2
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is there a leak btwn the eacv and the intake manifold?
maybe the gasket isn't sealing properly..
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Old 05-28-2004, 12:28 AM   #3
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Screw it all the way in, then back it out a turn. Get the car warmed up good, cause you can adjust idle while it's in warm up stage. Then adjust the idle with the screw. I made a mistake and adjsuted mine while it was still cold. Try that and see what happens. And I say spray throttl body cleaner on every thing on the intake that could possible have a leak. Cause if you hit it, it will suck up the cleaner and almost kill the car.
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Old 05-28-2004, 12:41 AM   #4
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if you use the product i mention below, hitting a vacuum leak will make the engine rev up.

BG Air Intake System Cleaner
Part No. 406

Net Wt. 14.75 oz. (600 ml)
Volume 19.9 fl. oz. Safely and rapidly removes accumulated deposits from the butterfly/throttle valve, throttle body and idle air control valves of the air induction system. Contains lubricants and anti-corrosion ingredients. Safe on oxygen sensors and catalytic converters.

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Old 05-28-2004, 12:23 PM   #5
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actually the idle screw wont do shit.......the computer has pre-determine the idle speed....its in the repair manual....it will automatically set the idle speed back. the only way the screw will work is if the management system is inactive.
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Old 05-28-2004, 12:32 PM   #6
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Quote:
Originally Posted by Preludetyper
actually the idle screw wont do s#$t.......the computer has pre-determine the idle speed....its in the repair manual....it will automatically set the idle speed back. the only way the screw will work is if the management system is inactive.

Fail.

The idle screw sets the idle, the computer adjusts the idle acording to the conditions, but it won't dial out your idle setting (not on OBD0 cars, OBD2 cars, and some OBD1, you can't even set it)


What the idle screw does:

There is a small passage, from inside the plenum, to the throttle body, it goes around, and bypasses the throttle plate.

The idle screw is set into this passage, and how far in or out it's set at regulates how much air can go around the idle plate.
Screw it in, it restricts the air more, and the idle drops.
Screw it out, and more air can flow past, and the idle rises.
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Old 05-28-2004, 12:37 PM   #7
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Bobnova hit it on the head as far as the idle screw function.

As for the pitch, my first guess would be vacume leak. Use the stuff that beehphy mentioned. It'll get you started...
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Old 05-28-2004, 12:52 PM   #8
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And something that goes along with what bob said. If you unscrew it to far it will act as a vacuum leak and give the up/down idle problem. I had that problem one time and it was the idle screw.

But again, spray the stuff beephy said and if you hit a leak it will rise. Spray the stuff I said and if you hit a leak the car will almost die.
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Old 05-30-2004, 08:32 AM   #9
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This is an old argument of mine with several members of this community. I'm talking about only the small idle bounce here not the massive ones.

#1 What make the idle speed bounce ? This is caused by a LEAN air/fuel mixture and is referred to as "hunting". ( even lawnmowers will do this )

#2 The TPS determines the amount of fuel being sent to the injectors at idle speeds. So all you can do is set the amount of air to be mixed with it.

#3 Although that screw on top of the throttle body is called a "idle speed screw" it actually is a "idle mixture screw". Yes, it does effect the idle speed but only by making it "RICHER" (lower idle speed) or "LEANER" (faster idle speed but will bounce if too lean) Yes..slipslap is correct, it can act as a vacuum leak. But...its a vacuum leak using filtered air ! ( turning it clockwise = richer.. turning counter clockwise = leaner )

#4 You actually can adjust the idle speed a little by playing with the stop screw under the throttle cable bellcrank on the front side of the throttle body. But you risk throwing off the delicate factory balance between the throttle plate opening and the TPS voltage output.

#5 I love this argument !!!

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Old 11-18-2010, 10:38 PM   #10
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i have the same problem too... ill check it tomorrow
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Old 11-19-2010, 02:00 PM   #11
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Wow old thread. Glad you searched. I found on my lude the EACV electrical plug was loose when fully connected. I don't know if the EACV plastic shrank, or the wire harness plastic expanded, but I could wiggle it and the idle would change and I could hear the air tooting in.

A piece of electrical tape strategically placed took up the slack space in the plug. No more wiggle room and no more EACV code. I don't know if this is your problem, but it sure was one of mine.
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Old 11-20-2010, 12:14 AM   #12
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i had a high pitch squeal like that, pissed me the hell of, drove me nuts. turned out to be in my throttle body base gasket, one of the vac lines on top of the tb was obstructed by a piece of dangling gasket.
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Old 11-20-2010, 04:56 AM   #13
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Quote:
Originally Posted by teamable View Post
i had a high pitch squeal like that, pissed me the hell of, drove me nuts. turned out to be in my throttle body base gasket, one of the vac lines on top of the tb was obstructed by a piece of dangling gasket.
explain more O_O.... because I checked all my lines they have no holes nothing -__-, plus they were all changed not too long ago.. what is this dangling gasket you speak of?..
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Old 11-20-2010, 04:57 AM   #14
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Quote:
Originally Posted by TripleLude View Post
Wow old thread. Glad you searched. I found on my lude the EACV electrical plug was loose when fully connected. I don't know if the EACV plastic shrank, or the wire harness plastic expanded, but I could wiggle it and the idle would change and I could hear the air tooting in.

A piece of electrical tape strategically placed took up the slack space in the plug. No more wiggle room and no more EACV code. I don't know if this is your problem, but it sure was one of mine.
EAVC electrical plug? which one is this?.. lol Im gonna search again..
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Old 11-21-2010, 05:50 AM   #15
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Ive never heard of a bad idle device on a 3g. Usually a good clean and replace the 'figure 8' oring and they are good to go. Check the resistance of the unit. It is basically just a solenoid, very little to go wrong, the ecu controls it by switching it on and off a hundred or so times a second. If the ecu is displaying a code, check the plug on the unit, may have broken a wire in the back of the plug.
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Old 11-21-2010, 05:52 AM   #16
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I have also had to repair a few ecu's that blew the driver transistor for the PWM idle. It may be an ecu problem as well
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Old 11-21-2010, 06:03 AM   #17
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An often overlooked vacuum leak is the seal between the brake master cylinder and the booster can.
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